Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$155.52	13.106%	$175.9025	$175.90	$175.90	$175.90
Purchase #2	$53.61	10.523%	$59.2514	$59.25	$59.25	$59.30
Purchase #3	$167.45	7.222%	$179.5432	$179.54	$179.55	$179.50
Purchase #4	$163.48	7.664%	$176.0091	$176.01	$176.00	$176.00
Purchase #5	$123.88	7.739%	$133.4671	$133.47	$133.45	$133.50
Purchase #6	$78.79	4.821%	$82.5885	$82.59	$82.60	$82.60
Purchase #7	$51.25	10.522%	$56.6425	$56.64	$56.65	$56.60
7 purchase totals =	$793.98		$863.4043	$863.40	$863.40	$863.40